Rotation of print data is well known in the art. The reason for rotating the print data is generally to enable printing a longer character line than is possible if the print line is not rotated; i.e., the width of the paper in the printer is fixed whereas its length is variable, particularly when using a roll of paper or continuous forms.
Rotation of print data is also well known in systems where the image data to be printed is serial and the printer has a plural element print head for printing data in parallel along a horizontal print line. Such a system is described in U.S. Pat. No. 4,084,195 for Image Data Remapping System to L. W. Pereira. In that system; however, it is necessary to buffer the entire image and thereafter strips of the image are successively removed and stored in a horizontal strip buffer. Rotation is accomplished as alternate bytes within a given byte column are transferred from the horizontal strip buffer into one of a pair of vertical strip buffers. The alternate bytes are removed from the horizontal strip buffer in groups which are stored in registers within the rotator. In the present invention a single random access buffer is used to store a column of image data. The column of image data, of course, does not exceed the length of the horizontal print line. There is no need to buffer the entire display image and remap as in the prior art. Column one of the display is printed as horizontal line one and this process repeats until all columns of the display are printed as horizontal lines. For further simplicity the printer is strobed by and receives clocks from the display whereby it operates in synchronism with the display but at its refresh rate. That is for each full image display, one horizontal line of printing is developed and transferred to the printer during vertical blanking and then a new horizontal line of printing is developed during refresh. The image is successively refreshed until all columns of image data have been printed as horizontal rows. Other prior art for manipulating image data by 90.degree. rotation but having the need to buffer the entire image includes U.S. Pat. No. 3,924,225 for Character Display Dot Raster Signal Generator Provided With Character Memory to W. Langnickel and 3,976,982 for Apparatus For Image Manipulation to E. Eiselen.